How do I resize an armature without ruining its poses?
You will have to scale the pose data's F-curves (you don't need to scale the armature and apply the scale then..):


You need to have keys for scale and location for every bone
Hide rotation f-curves for every bone (don't want to alter rotations)
Set pivot to 2D Cursor and position the cursor so the Y is 0 and X is any frame:


Select all visible (A). S+Y to scale animations/poses in pose space. Tadaa!